Recently, in the optical communications, research and development of the optical wavelength division multiplexing communications have been well-practiced for the way to dramatically increase the transmission capacity thereof and practical applications have been proceeding. The optical wavelength division multiplexing communications are in which a plurality of lights having a wavelength different each other is wavelength-multiplexed and is transmitted, for example. In such an optical wavelength division multiplexing communications system, an optical multi/demultiplexer is needed which separates a plurality of lights having a wavelength different each other from the wavelength multiplexed lights to be transmitted or combines a plurality of lights having a wavelength different each other.
One example of this kind of optical multi/demultiplexer is an Arrayed Waveguide Grating (AWG). The arrayed waveguide grating is that an optical waveguide part 10 having waveguides as shown in FIG. 4 is formed on a substrate 11, for example.
The waveguides are formed of one or more of input optical waveguides 12 arranged in parallel; a first slab waveguide 13 connected to the output side thereof; an arrayed waveguide 14 made of a plurality of channel waveguides 14a arranged in parallel, the channel waveguides being connected to the output side of the first slab waveguide 13; a second slab waveguide 15 connected to the output side of the arrayed waveguide 14; and a plurality of output optical waveguides 16 arranged in parallel, the output optical waveguides being connected to the output side of the second slab waveguide 15.
The channel waveguides 14a are a set for propagating lights that have been lead through the first slab waveguide 13 and are formed in length having a different setting each other. Number of the channel waveguides 14a constituting the arrayed waveguide 14 are generally disposed in multiple such as a hundred. However, in FIG. 4, to simplify the drawing, the number of these respective waveguides 12, 14a and 16 is schematically depicted.
To the input optical waveguides 12, optical fibers on the transmitting side are connected, for example, and wavelength multiplexed lights are lead. The lights that have been lead to the first slab waveguide 13 through the input optical waveguides 12 are expanded by the diffraction effects thereof to enter each of the plurality of channel waveguides 14a, propagating through the arrayed waveguide 14.
The lights that have propagated through the arrayed waveguide 14 reach the second slab waveguide 15 and are condensed at the output optical waveguides 16 to be outputted. At this time, the length of each of the channel waveguides 14a varies each other in a setting amount. Thus, a shift is generated in the phase of the respective lights after propagating through each of the channel waveguides 14a, a phase front of the condensed lights is tilted according to this shifted amount and the positions at which the lights are focused are determined by this tilted angle. Therefore, the positions at which the lights having a different wavelength are focused differ from each other, the output optical waveguides 16 are formed on each of the position at which the lights are focused and thereby the lights having a different wavelength can be outputted from the different optical waveguides 16 at every wavelength.
For example, as shown in FIG. 4, when wavelength multiplexed lights having wavelengths xcex1, xcex2, xcex3, . . . and xcexn (n is an integer of two or greater) are inputted from one input optical waveguide 12, these lights are diffracted at the first slab waveguide 13. Then, they reach the arrayed waveuide 14, pass through the second slab waveguide 15, as set forth, are focused at different positions according to wavelengths and enter the output optical waveguides 16 different from each other. Signal lights pass through the separate output optical waveguides 16 and are outputted from the end of the output optical waveguides 16. An optical fiber for outputting light is connected to the end of each of the output optical waveguides 16 and thereby each of the lights having a wavelength is separated and derived.
In this arrayed waveguide grating, improvement of the wavelength resolution of the diffraction grating is in proportion to a difference in length (xcex94L) of each of the channel waveguides 14a that constitute the diffraction grating. On this account, the xcex94L is designed large and thereby optically multiplexing/demultiplexing wavelength multiplexed lights having a narrow wavelength spacing is made possible, which could not be realized by a normally diffraction grating. Therefore, the function of multiplexing/demultiplexing a plurality of signal lights, that is, the function of multiplexing or demultiplexing a plurality of light signals having a wavelength spacing of 1 nm or under can be served, the function is required to realize the highly dens optical wavelength division multiplexing communications.
One viewpoint of the present invention is to provide a method for fabricating an optical waveguide. The method for fabricating the optical waveguide comprises:
placing one or more of substrates at a circumferential position on a turntable remote from a rotational center position in the radial direction;
rotating the turntable at a constant angular velocity of rotation xcfx89 in this substrate position;
moving a burner to and fro in the radial direction of the turntable between a position r1 in the radial direction of the turntable rotating and a position r2 on the side inner than the position r1 to reciprocate the burner across the substrates;
passing a material gas of glass, an oxygen gas and a hydrogen gas through the burner to generate a hydrolysis reaction of the material gas in a hydrogen oxygen flame; and
sequentially depositing an under cladding glass particle, a core glass particle and an over cladding particle on the substrates to form an optical waveguide part, wherein a turntable rotation speed r1xcfx89 im at the position r1 is set 600 mm/sec or above at least in the step of depositing the core glass particle in the steps of depositing the under cladding glass particle, the core glass particle and the over cladding glass particle.
Additionally, another viewpoint of the invention is to provide an optical waveguide and this optical waveguide is characterized in that the optical waveguide is fabricated by the method for fabricating the optical waveguide set forth.